I thought that NA was inglewood and NT was dallas and that the K was a different propeller?The P-51A and the A-36 (which is a P-51A with Dive brakes) have a turtledeck canopy and an airscoop OVER the propeller spinner and a 3-bladed prop. Allison V-1710-49 or later dash number engine.
The P-51B/C (B made in Inglewood and C made in Dallas) have a turtledeck canopy and the airscoop is less pronounced and UNDER the prop spinner and 4-bladed prop. Merlin V-1650-3 engine.
The P-51D/K (D made in Inglewood and K made in Dallas) have bubble canopies and the aiorscoop UNDER the prop spinner and a 4-bladed prop. Merlin V-1650-7 engine.
All of the above have a small dogtooth on the ing root where the landing gear retracts.
The P-51H has no dogtooth but otherwise looks similar to the P-51D/K with a bubble canopy and 4-bladed prop. Merlin V-1650-7 engine.